1. Field of the Invention
The present invention relates to a vibration type angular velocity detector used for vehicles, for example.
2. Related Art
A conventional vibration type angular velocity detector used for vehicles has driving piezoelectric elements, detecting piezoelectric elements and reference piezoelectric elements, which are affixed on vibration pieces. In this vibration type angular velocity detector, the vibration pieces vibrate in the x-axis direction as driven by the driving piezoelectric elements (driving vibration). When the angular velocity of the vehicle changes, the detecting piezoelectric elements detect vibrations resulting from a coriolis force acting on the vibration pieces in the y-axis direction (detecting vibration). The reference piezoelectric elements detect vibration of the vibration pieces in the x-axis direction. The angular velocity detector adjusts phases of outputs from the reference piezoelectric elements (reference vibration) to be in phase with the phase of the y-axis direction vibration. Finally, the angular velocity detector synchronously detects the outputs of the detecting piezoelectric elements as the angular velocity based on the outputs of the reference piezoelectric elements.
The driving vibration described above and the detecting vibration both act on the same vibration pieces. However, the direction of the driving vibration is perpendicular to that of the detecting vibration. When the coriolis force is F, the mass of the vibration pieces is m, the vibration speed of the vibration pieces is V and the angular velocity of the vibration pieces is .OMEGA., the coriolis force F is calculated as follows . EQU F=2m(V.times..OMEGA.) (1)
In Equation (1), the coriolis force F, the vibration speed V and the angular velocity .OMEGA. are vector quantities, and the symbol x represents a vector product (outer product). It is necessary to selectively detect the vibration based on the coriolis force F according to Equation (1) so that the angular velocity .OMEGA. can be determined. That is, only the detecting vibration should be detected. However, it is difficult to detect the detecting vibration precisely because of manufacturing processes for the vibration pieces. For instance, it is difficult to affix the driving piezoelectric elements and detecting piezoelectric elements on the vibration pieces so that the vibration direction of the driving piezoelectric elements (driving vibration) and the vibration direction of the detecting piezoelectric elements (detecting vibration) are perpendicular to each other. As a result, the detecting vibration includes a bit of the driving vibration.
In order to solve this problem, another conventional vibration type angular velocity detector is disclosed in JP-A-62-52410. This angular velocity detector only drives the driving piezoelectric elements so that the phase difference between the output of the driving piezoelectric elements and the output of the detecting piezoelectric elements can be kept at 90 degrees. This angular velocity detector also synchronously detects the output of detecting piezoelectric elements as the angular velocity .OMEGA. based on the outputs of the driving piezoelectric elements.
However, this angular velocity detector does not apply a y-axis direction exciting force to the vibration piece. Therefore, the output of the detecting piezoelectric elements may generate an output even when the angular velocity .OMEGA. is zero. That is, the offset may remain.